text:
Could gliders be a clean, practical alternative to other forms of transport?
Would it be possible to use pure gliders as an eco-friendly mode of transport?
From what I have read so far, gliders can travel at a speed of 100-170 km/h. That would not be able to compete with a jet plane, but it could easily be faster than a car, and possibly even a high-speed train, since it can fly directly and doesn't have to follow train tracks.
So, would it be possible to build a glider that fills this arbitrary set of requirements that would qualify it for regular travel:

It needs to be able to carry at least 30 people plus luggage. Otherwise the pilots are much too expensive.
It needs to be able to fly regularly, only being inhibited by severe weather.
It needs to qualify for international, commercial passenger service in all matters (safety equipment, radio, ...)
It doesn't need to be able to fly around the year, pre-plannable months without service are acceptable.
It doesn't need to work with current infrastructure, e.g. it would be acceptable if the plane needs special runways and/or launching mechanisms.

Would it theoretically be possible to build something like this?

It could be interesting for mountainous areas where road transport is inherently slow and energy intensive (lots of twists and ups and downs). This may not need to scale to 30 passengers if such shuttle would fly continuously during the day between mountain towns and villages.

Also, this could actually work better for freight, where schedule time can be more easily accommodated to external conditions.

Theoretically, yes. Practically, no.

Day to day weather is a huge factor in powered aviation. It is an even larger factor for non-powered aviation. You would not be able to satisfy the predictability and consistency needed to be a commercial scheduled carrier. At best, you may be a charter or sightseeing tour carrier.
No lift means no flight. Days of no or not enough vertical airmass movement would require canceling flights. Night time flights would be out of the question.
Faster flight and consistent lift may (I say again, may) be available in the jetstream currents. But, then you would need a pressurized cabin which adds more weight.
To make it commercially viable, the speed of transport would have to be significantly more than a car. Consistently faster than 100-120  miles per hour would be required to get people who already own cars to consider the added expense and hassle of air travel.
To make it commercially viable, after speed is considered, distance has to be factored in to get people who already own cars to consider the added expense and hassle of air travel. You would only attract people who are flying more than twice the distance of your clientele servicing diameter. For example, if it takes me 30 minutes or 30 miles to drive to the airport of departure, I would not fly to a destination that is less than 120 miles or 2 hours drive time away.
Competition must be considered in any commercial venture. Private land carriage like private cars would be a huge area of competition. So would public carriage like buses and trains. With increased technology reducing their ecological impact, these forms of transportation would be far more attractive than a proposed glider.
Most gliders efficient enough for consistent cross-country flights have interiors that are small, cramped, not climate controlled, and require the pilot and passenger to sit in an almost reclined position for the duration of the flight. Larger gliders like those used in WWII were larger, cumbersome, and required huge aircraft to lift them airborne. The military has already abandoned such projects for troop transport.
Trans-oceanic flights would be not at all practical if at all feasible.

This does not mean that it should not be attempted. You should know the obstacles in front of you and try to overcome them. Your failure might lead to someone else’s success.

Good answer.  I would just add two things:  it still takes fuel to get the glider to altitude, (so not clean) and the probable lack of willingness on the part of passengers to fly regularly on a craft with no go around capability.  Also, too encouraging at the end!  ;)

@MichaelHall I would argue that 1) a glider is still cleaner 2) gliders don't explode on impact

@Abdullah, if you were to calculate the theoretical fuel required to tow a 30 passenger glider to altitude, and plot the range achieved in a glide against a turboprop covering the same range in the most fuel efficient manner you might find a small advantage.  But likely not enough to negate my point or prove this as a viable idea.  Good point about fire safety, but I’m still betting against this idea “taking off”...

@MichaelHall well, soaring gliders have a chance of unlimited range.......that's what I was referring to. I mean, think about migrating seabirds. In any case, the tow plane could be an EV without compromising the range with it's heavy battery! Ah, that's one important thing.

“A chance” is the key word here...  How many paying passengers would be willing to sit for hours as the pilot seeks out the thermals that just might allow them to reach their destination?!

...and flying "direct" factored into the speed calculations stipulated in the question.

@Abdullah - Gliders have a theoretical chance of unlimited endurance during daylight hours when there are still thermals. Their range is less practical. To get the theoretical endurance, you would have to chase the thermals in whichever area and direction they happen to be. That’s not much certainty and consistency for a paying customer who has expectations and deadlines.

It doesn't take an explosion, @Abdullah, to kill passengers.

Let's also remember that turning in circles for 20 minutes is not a pleasant experience for most and you will likely have some inexperienced passengers throwing up

Good answer but many of these points are much less of an issue for freight:

weather, schedule and distance to airport are much less of a problem if merchandise can wait,
pressurization : could probably be avoided for many types of freight,

Also, in mountainous areas where road transport is inherently slow, expensive and more dangerous, this may be even more advantageous.

@LaurentGiroud - In today’s world, time means money. Even freight is on a time clock. In mountainous regions, you would need space for takeoff and landing. It may be just as hazardous to fly, takeoff and land a heavy glider in those regions as it is to drive. Mountain flying is different than other flying. There is very little recourse if you get too low. Also, the largest glider produced, the XCG-20 (a C123 Provider without engines) still only had a 14:1 glide ratio. The proposed purpose was to use it as an airborne freight train with multiple in tow behind an airplane. The idea was abandoned

@DeanF. that's a good point. However, with energy prices likely to increase significantly in the not too far future (peak oil, CO2 taxes, not enough renewables to replace fossil fuels) the balance is likely to shift significantly eventually in favor of low energy transport.

@LaurentGiroud - Maybe. It is far more likely that airships will be used instead of gliders. There is far less likelihood of landing-out in an airship. Imagine trying to make an off-airport landing in an aircraft the size of a C130. Especially since that aircraft would have to have much longer wings to achieve a respectable glide ratio. Even highly skilled glider pilots in highly efficient competition sport gliders occasionally land-out. The airborne freight train is intriguing, though. That would still require power.

There's one thing that will forever prevent an unpowered aircraft from entering commercial passenger service: the inability to make a second attempt at a landing.
Airliners, with all their instrumentation, very experienced pilots, and such don't make go-arounds frequently -- but especially during weather, they do make go-arounds.  A passenger sailplane absolutely can't make a go-around, so if it gets crossed up due to a crosswind gust low and slow, instead of advancing throttle and climbing out, all the pilot(s) can do is pick where and how hard to crash.
This complete lack of second chances, as much as any of the other objections raised in other answers, will ensure that unpowered aircraft will never see commercial service.  It can also lead to "landing out" where you wind up having to retrieve your passenger glider from a farmer's field, freeway, or worse, along with its payload and crew.
The other big issue is how to launch these immense sailplanes -- with a common sport glider or competition sailplane, you're towed into the air by either another airplane, a winch, or occasionally a car or truck.  The winch that could launch something the size of a 737 high enough to fly off in search of its first lift would be so big and expensive it would severely limit the number of airports that could service such craft.  The airplane that could do it would be at least as big as that 737.
Comments suggested a one-time use rocket engine as emergency power to allow go-around -- but this isn't practical.
The engine required would need to have thrust comparable to maximum power for both 737 turbofans, and burn time long enough for the 737 sized glider to climb from low final to at least pattern altitude (ideally to the same altitude it would initially tow to).  This gives an engine comparable to the Castor 4A-XL boosters used on the Japanese HII-A orbital launcher -- engines a meter in diameter and about twelve meters long.  These would be bigger and heavier than both 737 engines combined (though lighter than those engines plus full fuel), weight and drag that would be carried on every tow and for the full duration of every flight, but which would contribute only in the case of needing a go-around.  And this engine, once ignited, can be neither  throttled nor even shut down before it has burned all its fuel.
You're surely better off with the two turbofans now used for takeoff, climb, and cruise.

"inability to make a second attempt at a landing": It looks like the definitive answer! Even Greta would agree.

A one-time-use rocket motor might be kept in reserve as a simple and inexpensive way to address the second-chance-at-landing issue-

Interesting thought.  How long does it take for a 737 to climb from low final to pattern altitude?  How much thrust is needed?  Since your description requires a solid propellant type ("simple and inexpensive") it can't be shut down once ignited, and I think you'll find it won't be either simple or cheap (hint: it's going to be bigger than the Castor boosters on Atlas orbital launchers, and you have to carry that weight from takeoff to landing on every flight).  Not going to stand in for having an actual engine, I think; probably heavier and would require replacement any time you go around.

@quietflyer Current Castor 4A-XL engines are about 12 m long a 1.02 m diameter, making them bigger than both 737 engines combined.  Not to mention what happens if it fails (much worse than a turbofan failure).

Sink speed scales with forward speed. To make regular thermals useable, the flight speed and wing loading would be that of a regular glider. Also, thermals have a limited diameter and adding passengers will make the resulting airplane too large and too fast to gain any height even in strong thermals.

This does not seem like a major issue, the aircraft would only need to store enough energy to propel itself for a second landing attempt. A (few) retractable emergency hydrogen (or any other energy dense fuel) powered propeller(s) is all it would need to ensure that second attempt in all conditions. The impact on weight would likely be negligible.
A rocket of such power seems unnecessary.

Impact on weight for a power system to allow a climb to pattern altitude from low/slow?  Definitely not negligible.

A pure sailplane is probably impractical for commercial aviation, for all the reasons others have given. But, just as there are proposals to add sails to commercial shipping to reduce fuel use, maybe flight paths of commercial aircraft could be actively modified to allow them to make use of soarable atmospheric conditions, such as high-altitude waves.  Increasingly accurate meteorological forecasts combined with artificial intelligence could perhaps make this routine and effective.

Eastbound flights will take longer routes to take advantage of the jet stream, so this is already factored in. Westbound flights will take longer routes to avoid the disadvantage of the jet stream headwind. Plus, with pax demands for flights to be on time, especially for annoying little things like making a connecting flight, there often isn't time to loiter or wander looking for thermals. Hard to imagine this being able to be efficiently factored into commercial flight schedules.

Well new twin engines airliners are already some impressive gliders... The glide ratio (GR) of the A320 is around 17 and the new 787 GR is above 20. Those numbers are quite impressive considering the two big engines shut down adding a lot of drag. Without engines they could probably reach the lower limit of aerobatic gliders with a GR of around 25 to 30.
I could also add a safety issue to the previous answer. Every landing in a glider is mandatory. Without engines you don't have any opportunities to go around or wait in the pattern for the runway to become available. This restrict even more the weather in which you can fly, too much cross wind and it is way to dangerous to try.
Finally saying that a glider can fly directly is only partially true as it still requires to find thermal ascending current to extend it's range. In a glider you know when and where your taking off, but it's hard to say the same for the landing, not really good for commercial ops.


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Why does the MD-87 have strakes on its engines?
Apparently, the MD-87 has a strake on both engines:

Source: Airliners.net
If I'm not wrong, the engine strake attaches the airflow at high angles of attack on the wing. But in this case the engine is behind the wing. So what is the purpose of this little fin? Is it a strake or something else?

Flow separation always produces considerable drag. So even though it is behind the wing, and would not affect lift, flow separation is still undesirable here.

They are indeed strakes which serve to reduce flow separation on the lower rear engine fairing by creating a vortex which will mix the outer, faster flow with the slowed down boundary layer on the lower rear part of the fairing. You will notice that the nacelle is mounted at an angle of 3 degrees to the fuselage: This is to position the intake and nacelle in line with local airflow, which is pointing slightly downwards at the rear fuselage due to the wing's downwash. The exhaust is again pointing directly back, so the thrust will be aligned with the lengthwise axis of the fuselage and will not produce pitch moment variations when thrust is changed. In combination with the nacelle incidence this produces a more pronounced curvature on the lower side of the nacelle, which in turn is more prone to flow separation.
You could as well place a row of vortex generators on the bottom of the fairing, but the strake will produce less drag when downwash is low and its service is not needed. With higher downwash, the strake will produce a stronger vortex, just when it is needed most.

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Why was the A380 built with a gull-wing design?
I've noticed that the wings on the A380 are very curved in comparison to the 747. I mean the 747 has a lot of wing flex but the A380 has less wing flex and the wings are flexed down in comparison to the 747. Here there are two photos that might help you understand what I'm writing. So why are the A380 wings like that and what are the benefits?
Source

Source

I don't know that comparing the 380 to the 747 would be good, either, because the design philosophy may vary, due to temporal and material design differences.

Oh yes. The A380 has a little bit of wingflex but the 747-8 for example doesn't flex down the wings as much as the A380.http://mileagegenius.com/wordpress/wp-content/plugins/Archive2/cache/b6e57_130416114126-lufthansa-gallery-water-cannon-horizontal-gallery.jpg

@JonathanWalters The differences in philosophy and materials is the point of the question.  I think the original comparison was far more interesting than this.  Yes the 787 and a380 have different philosophies, what's fun is knowing all the details as to why.

The wings are designed like that. You can see them in the picture below.

Image from airliners.net

The A380 wings are designed to be the most efficient while still inside the 80m 'box' for efficient airport operations. The result is a clean slate design which used CFD extensively to get the most efficient aerodynamic design possible.
The 'curve' near the root means that the landing gear in the wings could be as short as possible while being long enough to prevent a tail strike during rotation and allowing the spar to pass below the floor.
The shape also allows enough ground clearance for the inboard engines. This assumes importance with the advent of engines with ever higher bypass ratios.
Of course, the use of modern composite materials means the the wing 'flexes' up to be more or less straight once the aircraft is airborne.

(wikimedia.org) In-flight 'flex'.

The A380 has a gull-wing design. This has some economic benefits, the main one being shorter landing gear while giving enough ground clearance for the engines.

Aeroalias answer already covers most points. Still it may be worth to add that its not a clear gull wing, but more toward a dihedral setup with an increased volume at the front root part. This is most obvious when looking at it from the back while flying.
There are not many pictures showing one flying and from behind but this (taken from Wikipedia) might give a hint:

Beside the already mentioned advantage of shorter and thus lighter landing gear and more room for engine mount (much like the Ju87 inverted gull wind gid provide),
a dihedral wing also increases lateral stability in flight.
Increased comfort was as well one of the ambitious design criteria for the A380. Who ever had the chance to board one did enjoy the results. So considering the many, often each other contradicting requirements for wing (and fuselage) design, this marks a sweet spot - at least when reaching a certain size :))

That right-hand wing tip, and the presence of at least two people just under it, doesn't look too comforting...

Regarding pictures showing A380s in the air photographed from behind, Wikipedia seems to have a few.

@aCVn Great, thanks.

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What is this object on an MD-11?
There is something above the engine on the tail of this MD-11:

What is that?
Source

They all have that,  it's part of the fairing. Are you asking what is purpose is,  or why it's on that particular aircraft?

That is the pylon that supports the engine. More details in  Quora

You should provide the source of your image, a direct link to the page containing the image and the author information. You forget nearly systematically to do it, and from a legal standpoint this is not possible (and in my opinion not ethical either). Here is an example.

Possible duplicate of:   https://aviation.stackexchange.com/questions/51883/what-is-this-tab-above-the-dc-10s-2-engine

As was said in the comments above, it is the support structure for the engine as seen in this drawing:


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Do contra-rotating props have worse tip vortices than single props?
As I understand it, blades from a propeller have their own tip vortices, because the blades produce lift via the same aerodynamic principles as wings. So they must have tip vortexes too.
So with contra-rotating props, e.g. the NK-12, do the tip vortices interfere with each other in a good or in a bad way? Is their nature somehow better than those from single props?

Counter-rotating props are designed such that the second rotor should remove the swirl component of velocity that results from the parasite drag on the blades.  This improves the efficiency.
Think of the counter-rotating blades as a single actuator disk (imagine the two rows being very close together) -- and then compare the counter-rotating actuator disk to an actuator disk made up of single-rotating propeller.
If the two disks have the same thrust and same diameter and same load distribution, then we would expect them to have the same induced power and the same strength tip vortices.
The viscous (parasite) power differences will depend on the number of blades, their chords, and several other details -- we'll assume it is the same.
So, if the counter-rotating disk can recover the swirl energy, it will be a more efficient system with the same tip vortex strengths.
That said, in a finite-blade system, the second row of blades certainly intercepts the wakes from the first row.  This causes a great deal of noise and is one of the primary reasons you do not see counter-rotating props widely adopted.  It is also the reason modern counter-rotating props typically have a different prime number of blades on each row -- 5,7 or 11,13, etc.


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What are these fins on the Beechcraft 1900?
Here's an image for you to see these little fins. What are they used for?

Source (image has been modified to indicate location of fins).

Related: http://aviation.stackexchange.com/questions/3382/why-dont-horizontal-stabilizers-have-winglets/11784#11784

Well, those fins were put there to increase yaw and pitch stability on the D version because of the change in the centre of gravity due to a higher fuselage from the C version. This D model also had more powerful engines than the C model. To add on, the strakes at the bottom were added for the same reason too.
More info can be found here.

Almost correct! The 1900 has a higher fuselage than the King Air, this made those fins on the horizontal tail necessary.

You might also add that the D model (pictured in the question) had more powerful engines necessitating some of the modification from the C model.

That's a crapload of additional drag just to make the thing fly well. Seems like bad design.

Well, it wasn't the original design... and it's a lot cheaper to redesign King Air into the 1900 than to redesign an entire new aircraft. Would your customers like a marginally higher fuel bill, or would they prefer to pay twice as much for an aircraft built to a new design?

Considering the fuel bill will eventually add up to far more than the price of the aircraft for an airline, I would think the later.

Some of the answers are referring to the dual aft strakes on the underside of the fuselage below the tail. The dual aft strakes are  Indeed there to increase stability, specifically  for one engine operations. They remove the yaw damper limitation. To answer the question, the 1900 has the same horizontal stabilizer as a King Air 200. Obviously the 1900 is far longer and bigger than the King Air 200 and needs those extra modifications on the tail. Basically it saved Beechcraft from redesigning an entire new tail, saving quite alot in design costs. Both the C and D models have the “fins” you have circled in your picture. If you think that the dual aft strikes are a bad design, you are completely wrong. Operators actually pay huge amounts of money to fit them to older model King Air 200s part of the Raisbeck upgrade. They improve efficiency and as mentioned earlier remove any yaw dampener limitation.

What is the yaw damper limitation?  Is that that flight is prohibited if the yaw damper is out of service?

By the way: welcome to SE!

The lower strakes prevent flow separation at high angle of attack, which only shows what a poor design the original aft fuselage is.


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Why does the MiG-15 have a cruciform tail?
The horizontal stabilizers of the MiG-15 are halfway up the tail. This is called a cruciform tail.

Why did they put them there? Why not a T-tail or the normal tail where the stabilizers are on the fuselage?

Well.. not a normal tail because that is where the exhaust from the jet engine comes out. You would have to have a lot of structure there in the exhaust stream to mount the stabilizer, or the fuselage would need a very different shape in that area.

@RonBeyer I don't think it's that obvious. The control system, whether hydraulic or something else, must run into that small tail fuselage and get up into the tail. Seems not that hard to put the stabilizers on the fuselage.

It isn't so much the control system, but the structural components. There is a spar that needs to be there to support the loads and to design that around the exhaust would add quite a bit of weight/complexity. On top of that, where you would mount them is where the speed brakes are.

For a couple of reasons.
First the shaping of the aft fuselage does not offer the space to accommodate the structure for the tailplane and flight controls without adding on an additional blisters to provide space.  The routing of the jet pipe further uses up space as compared to an F-86.  See images below.

A low mounted tailplane would not have a clean airflow over it due to the MiG-15's middle mounted wing as opposed to the F-86's low wing design.

Didn't even realize the F-86 tail is almost exactly what I envisioned.

And do notice how the F-86 does have a thickened and flattened section of fuselage right where the horizontal stabs are fitted in order to facilitate the cables and structural components (afaik the controls were all mechanical, not hydraulic, in both aircraft).

The tail position is a compromise which is influenced by these factors:

Interference with the wing's wake: The tail should be outside of the boundary layer flow coming off the wing root at all normal angles of attack. A high tail can cause a deep stall, something that was not known in 1947. Today all similar designs try to get the tail surface below the wing's wake.
Lever arm: By mounting the tail higher up on the swept vertical tail, its lever arm (in horizontal direction) can be increased without lengthening the tailpipe. A longer tailpipe means more mass and more internal drag and is best avoided.
Flutter: The higher the horizontal tail is along the vertical, the higher the danger of flutter. Here the longer lever arm (now in vertical direction) will lower the eigenfrequency of the bending mode of the vertical and the torsion mode of the rear fuselage. I suspect that for that reason the full T-tail was not chosen.

Mounting the horizontal smack in the middle of the tailpipe would require a heavy spar there to carry the bending moment across the fuselage. Mounting it on the vertical tail allows for a much lighter construction.

It’s a good question. I remember that during lectures on aircraft structures, it was stated that the horizontal tail should be mounted either at the fuselage or at the top of the vertical tail. Not in between, since that involves having to implement the downsides of both methods.

The case of the Bae 125 was mentioned: this was designed as a full T-tail, but during flight tests it turned out that additional vertical tail surface was required which was put on top of the existing structure.
Wikipedia mentions that the design of the MIG 15 was based on that of the Focke-Wulf TA 183 Huckebein, which was only built as a wind tunnel model implementing a serious T-tail, not a cruciform. It seems probable that development of the MIG 15 vertical tail had a similar history to that of the Bae 125.

The MiG-15 was helped along by ex-Heinkel engineers, so the Ta-183 heritage is very doubtful.


text:
What is required to be an "FAA-qualified helicopter aerobatics pilot"?
Chuck Aaron is the only FAA-qualified aerobatic helicopter pilot - How'd he do it?

What requirements does one need to meet in order to perform aerobatics in a helicopter?  Specifically, the training/qualifications and FAA paperwork necessary.
Who certifies said pilot, if there is no one certified themselves to do so?

forget about the pilot and the FAA. what you need is an aerobatic capable heli, which is one that has a rigid rotor system. http://en.wikipedia.org/wiki/Helicopter_rotor#Rigid

I have no idea how significant this is, but the FAA's online record doesn't make any mention of aerobatics

I think this depends on what "FAA-qualified" means: the FAA defines aerobatic flight in 14 CFR 91.303 but it doesn't issue any pilot certificates or ratings for aerobatics. I did find several references to FAA Form 8710‑7, Statement of Acrobatic Competency (e.g. here), but the form itself isn't even listed on the FAA's form page.
There is an FAA document called Guidelines for Pilots Seeking All-Attitude Training which states that there is no special certification required:

[...] no separate certificate, rating or endorsement is required to
  specifically qualify an individual as an all-attitude instructor

And:

Anyone claiming to be an all-attitude instructor must at least hold a
  valid Commercial certificate if working for compensation or hire. The
  instructor must also be a certificated flight instructor (CFI) to
  provide FAA endorsements. Other than that, CFI credentials are not
  necessary for anyone to claim to be an all-attitude instructor.
  Therefore, caveat emptor - buyer beware - applies when seeking
  instruction.

Although their definition of "all-attitude" isn't exactly the same as "aerobatic", the document seems to make it clear that aerobatic training is not directly regulated. And looking through a variety of aerobatic websites including the IAC one, there is no mention of any required FAA certification. Endorsements for tailwheel, high-performance or complex aircraft are often required, but that's because of the aircraft itself, not the aerobatic activity.
But this profile gives some clearer information:

Once the helicopter was ready, the FAA needed to certify it in order
  for Chuck to perform stunts with it. Once the aircraft was certified,
  the next step was to also get him certified, which ended up being a
  complicated process. The FAA was not sure how they could certify him,
  so they turned to Rich Lee, chief pilot for Boeing, who evaluated him.
  “He wanted to make sure that I did have all my screws in my head and
  that they were not loose”, said Chuck, laughing.

My guess is that the FAA first issued a new airworthiness certificate and/or waiver for the modified helicopter. That's very common and it would be same for a home-built aircraft, for example. Second - and this is a guess - they had the Boeing guy evaluate him for the Statement of Acrobatic Competency that I mentioned above. Although I can't find it on the FAA site, it obviously existed in the past and if you look at this example from the EAA Warbirds site, you can see that the evaluation process was (is?) 'outsourced' by the FAA anyway, presumably because they have no experts available internally:

I desire to take advantage of an FAA procedure for the evaluation of
  my competency by a Warbird Aerobatic Evaluator (Warbird Evaluator) on
  the list maintained by the EAA Warbirds of America, Incorporated.

I suspect that putting a unique airworthiness certificate together with a unique Statement of Acrobatic Competency resulted in a uniquely "FAA-qualified" acrobatic helicopter pilot.
Finally, according to Aaron's LinkedIn page he is the:

First FAA Certified Helicopter Pilot to recieve a Helicopter Aerobatic
  Certificate from the FAA.

That again seems to emphasize the helicopter, not the pilot.

Well Aaron's wiki page cites a Wired article written about him, which does claim "He is the only pilot in the United States licensed by the Federal Aviation Administration to fly aerobatics in a helicopter"

Does this imply that any helicopter pilot who feels confident enough can just decide to do a flip?

@raptortech97 If you follow the rules in 91.303 then I suppose you can. Of course, if you mess it up and survive to have an interview with the FAA, then 91.13 (careless and reckless operation) and 91.9 (complying with the operating handbook) will probably come up in the conversation :-)

@erich After thinking some more, it might mean that the FAA has given him a waiver for certain activities. The FAA issues various types of waiver to allow exceptions to specific regulations, and possibly he's the only person to get a waiver related to helicopter aerobatics. Lots of FARs include the wording "unless otherwise authorized by the Administrator...", so perhaps that's what's going on. But it's a complete guess and I couldn't (quickly) find anything to support it.


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Is a night VFR rating a prerequisite for an EASA CPL?
I'm wondering if I need to pay for a night VFR (NVFR) rating or can I just do my time building, ME, IR and exams to get a CPL? Is it possible without an NVFR rating?

According to FCL.610 (IR - Pre-requisites) you need to have a PPL or CPL and a night rating to apply for the IR.
If you do not have the IR, the night flying qualification (NFQ) is no requirement to start training for the CPL. According to the AMC appendix 3 of the Notice of proposed Amendment (NPA) No. 2008-17B night flying is part of a training course for the CPL.And FCL.315 states, that the applicant for a CPL shall complete a trining according to the appendix 3, cited above.
SO: If you have the IR, you should also have the NFQ but you do not need the NFQ to start training for the CPL.
However, you only need 5 hrs night flying to get the NFQ and there is no examination, i.e. the FI rates your skill.

It is possible (at least in 2019). The mentioned in the previous answer FCL.610 (IR - Pre-requisites) (see Part-FCL) clearly states that for IR you need NVFR only if you are not going to fly at night:

Applicants for an IR shall:
(a) hold: (1) at least a PPL in the appropriate aircraft category,
and:
(i) the privileges to fly at night in accordance with FCL.810, if
the IR privileges will be used at night; or
(ii) an ATPL in another
category of aircraft;
or (2) a CPL, in the appropriate aircraft
category;
...

So for IR it it possible, but you will not be able to fly at night even though you might have a valid IR.
But the CPL is a different story. If you are following a modular course (and from your question I can conclude that it can be only a modular course - integrated one does not allow you to decide whether you want NVFR or not), you must undergo 5 night instructional hours during your CPL training if you hold a valid IR. it is stated in the Appendix 3 -Training courses for the issue of a CPL and an ATPL, part E. CPL modular course -Aeroplanes, subpart "Flying training", #10.
So when you finish your CPL and IR during the modular course, your will have a NVFR somehow. It is not just 'time building' though, there are some requirements about dual time.


text:
Should DUAL flight be logged as SINGLE PILOT TIME?

Should DUAL flight be logged as SINGLE PILOT TIME?
Should total SINGLE PILOT TIME + total MULTI PILOT TIME = TOTAL TIME?
In what cases SELF could be specified in PIC NAME on DUAL flight?

EASA regulations applied! (Hungary)
Many thanks

Which country's regulations are you asking about? If it's the US, we have some questions that might help: here, here.

1) If you are under training in a single pilot aircraft (e.g. C172), it is logged as dual in single pilot. If you are under training in a multi pilot aircraft (e.g. A320), it is logged as dual in multi pilot.
2) Correct.
3) If dual (under training), the PIC name should always be the name of your instructor. The only time you use SELF is if you were PIC, and therefore the flight cannot be dual.
See EASA Part FCL; FCL.050: https://www.easa.europa.eu/sites/default/files/dfu/Part-FCL.pdf

I'm not challenging your answer, but it would be great if you could link to the underlying regulations. On this site we have a general preference for including sources and references where possible.


text:
Can I work on aircraft without an A&P license?
Can I work at a place where I pull parts, drop engines, hang engines which get sold back into the aircraft market? Am I allowed to do so without a A&P License? I've been told that it is legal if you're supervised. If so what is considered supervision? I live in California with no aircraft schooling at all if that matters.

Supervision means under the direction of a licensed A&P, but yes, you can. The A&P is the one who needs to sign the log books for the work performed, so they are ultimately responsible. This is exactly how you build hours to get your A&P.

There are several books all mechanics must know about that you can likewise mine for knowledge. I would suggest, for a start, Aviation Maintenance Technician Handbook—General; the Airframe and Powerplant Mechanics Powerplant Handbook, AC 65-12A; and the Airframe and Powerplant Mechanics Airframe Handbook, AC 65-15A. They are free on the FAA website.

Anyone can work on a plane.  Only an A&P can certify the work and return the airplane to service, with a few exceptions.  A plane cannot (legally) fly unless the work has been signed off by an A&P, with a few exceptions found in pt43 Appendix A Para C (preventive maintenance).  Even if the work is allowed by pt43 App A Para C, the person performing the maintenance must be at least a private pilot, the airplane must belong to (or be operated by) that pilot, and the airplane cannot be in commercial service.
"Supervision" is loosely defined and is up to the A&P to decide in the field.  The idea is that the supervising mechanic should be observing while you work but the language allows the mechanic to determine exactly what must be observed while work is being performed.  Some will want to be over your shoulder the whole time, some will trust your word, but most are somewhere in the middle (trust but verify).
You may work in a shop as an apprentice and do all of the work you describe but you will be subject to the directions of your supervising mechanic.  Your time as an apprentice counts toward A&P certification, too.  They will likely start you at very low pay and assign menial tasks until you prove yourself to be reliable.  Sweep the floors with a smile and don't be offended that they don't throw cylinder replacements at you on day one.  You need to build up trust before shops will let you do any fun work on customers' airplanes that can easily exceed the price of most middle class homes.

“Only an A&P can certify the work and return the airplane to service, however.” Not true. There are lots of things per Part 43 “(f) A person holding at least a private pilot certificate may approve an aircraft for return to service after performing preventive maintenance under the provisions of §43.3(g).”

Also not true, “airplane must belong to that pilot”. The airplane must be operated by the pilot. If I rent a plane from a flight school and it needs any of the maintenance in Part 43 that I am allowed to do, e.g landing light, spark plug cleaning, replace a flat tire, etc. then I can perform the maintenance. Also, Part 135 operators have specific list of things in their Op Specs that their pilots are allowed to do in the field.

I think supervision is pretty much spelled out in the Part 43. “if the supervisor personally observes the work being done to the extent necessary to ensure that it is being done properly and if the supervisor is readily available, in person, for consultation.” I have been working on my own planes since 2000 and every A&P I have worked with insists on being in the hangar when we do anything except the items in Part 43—preventive maintenance. There are probably A&Ps out there that bend the rules, but the ones I know value their certificate too much to risk losing it with unsupervised work.

Regarding first comment: hence the PM carveout. This question is not asking about pt135 so I did not address it. I'll make the revisions to this answer based the other points you made. And yes, there are many A&Ps who bend the rules.

@JScarry FAR 43 isn't really prescriptive - "to the extent necessary" is really entirely up to the mechanic's discretion (and their confidence in the person swinging the wrench), and the readily in "readily available, in person" has wiggle room: Certainly being in the hangar is "readily available", but being in the office doing paperwork or on the ramp changing a tire could also qualify since you could easily call them over if needed. (The paperwork is perhaps more "ready" than than if they're in the hangar but elbow-deep in work on another plane when you need their consultation.)

+1 for sweeping floors alone. Crucial task but so many people think it below them.

You can, but on a certified aircraft, you will need your work reviewed and approved by a licensed A&P which will be documented as such in the airframe, powerplant, or propeller logbooks.
On the other hand if you own an amateur built, experimental category aircraft which you completed at least 51% of the construction on, you are allowed to do your own maintenance on that aircraft without A&P signoff. A&P and Repairman can sign of conditional on experimental. Anyone can work on experimental.

If you own a special light-sport aircraft (S-LSA) you can also obtain a repairman‘s certificate that allows you to work on that particular class of airplane. See §65.107   Repairman certificate (light-sport aircraft): Eligibility, privileges, and limits.

One minor nit. In order to perform maintenance on an experimental aircraft  that you built, you need to get a repairman certificate. It will allow you to do maintenance without an A&P signoff, but you will still need an IA to do the annual condition inspection.

I'm curious as to how the 51% is defined.


text:
Do pilots ever suffer PTSD after emergency landings?
I have watched a few documentaries about plane crashes where the whole crew and passengers survived. Of course the passengers are usually all scared, but what about pilots?
Do they ever suffer from Post Traumatic Stress Disorder (PTSD)? Are they ever too scared to fly again after such landings?

Of course they do. Pilots are human too. That said, it will obviously vary tremendously from individual to individual. I'm not entirely sure what sort of answer you are looking for here, perhaps you could clarify?

Well , In the film "Sully" the pilot wants to go flying again as soon as it is possible. Yes I'm aware that this is just a fabularized version of the actual events that happened.  I've never heard of any pilot that e.g never went flying again after because of being scared. Maybe you could give me an example?

I find a safe landing fairly traumatic! It is just a controlled crash after all :)

@Miko https://en.wikipedia.org/wiki/Scandinavian_Airlines_Flight_751 comes to mind. The captain never flew again.

Pilots suffer from all the same issues passengers do, and more. PTSD, Survivor Syndrome, remorse,  guilt, irrational fears, nightmares, etc. This is highly dependent on the person as well, some cope much better than others, while some may never fly again after relatively small incidents or scares.

I've been close to a couple of training accidents, thankfully with no serious injuries.  In both cases, the CFI got them up and flying again as soon as possible, in one case, about an hour later.  I don't understand the psychology but apparently it's common practice.

Yes, for a while: Capt. Al Haynes, after saving 184 lives on United Flight 232.

I was lucky enough to have dinner with Al Haynes a few years ago, and he told me that he had a very difficult time overcoming the guilt of the disaster. The talks he gives have been a way of coping.  (As a side note, he also donates all the money he receives from the talks to the survivors of the crash).
Capt. Haynes has said the same thing in various interviews:
The Seattle Times:

Haynes said it took many sessions with a psychiatrist to overcome his
survivor’s guilt. He resumed flying three months after the accident;
mandatory retirement at 60 followed two years later. [link]

NY Mag:

It was very hard to get past the guilt of surviving. My job had been
to get people from point A to point B safely, and I didn’t do it. I
felt that I had killed them. I had a lot of psychiatric help at the
hospital and afterward. Finally, one psychiatrist said, “You’re not
going to find an answer. You just have to accept that it happened.” [link]

AvWeb:

Haynes said, at the time, that he remained troubled by the accident
and constantly wondered if there was something he could have done,
some overlooked decision that would have saved all aboard. [link]

Before his death, Denny Fitch said something similar:

"To find out 112 people didn't make it, that just about destroyed me,"
Fitch once said. "I would have given my life for any of them. It was a
really tough time." [link]

Before I entered flight training I was stashed as an Ensign at the Legal Department at NAS Corpus Christi. I remember reading an accident report for an A7-E pilot who had been cleared for takeoff. Shortly after he began the takeoff roll a crash truck was cleared by ground control to cross his runway. They met a little past mid-field. The investigation stated that the pilot ejected just before impact, and had one swing in the chute before reaching the ground.
What interested me was that he was interviewed in the hospital soon after the accident. The psychological trauma was severe enough that he stated he had no memory of the incident. That he remembered the roll down the runway, but from reacting to the truck and ejecting, to waking up in the hospital, he had no memory. The memory is there, just not acknowledged.
In 1981 aboard the USS Nimitz there was a horrible accident involving an EA-6. I was on the flight deck when it crashed into the six pack. The six pack had 6 fully fueled, and armed F-14's. They were carrying Sparrows, Phoenix and AIM-9's that cooked off from the massive fireball that followed the crash. 14 men died. I helped fight the fire, and helped pull a crew member out of the crash. This story has changed in its telling over the years. Today there is a very deep sense of sorrow, and I don't want to remember, but it has been impossible to forget.


text:
Why does avgas 100LL smell different than automobile gasoline?
Why does avgas 100LL smell differently than automobile gasoline?  And why don't avgas 100LL fumes from a fuel tester located in the cabin make pilots ill?

Why are you sniffing avgas?

The sweet smell of 100LL AvGas is due in large part—if not entirely—to the additive Tetraethyllead (TEL). TEL is included in the formulation of 100LL as an anti-detonation additive, octane booster, and lubricant.
A fuel tester stored in the aircraft cabin should not induce crew illness because the tester should be drained of all but residual fuel, that residual fuel will evaporate very quickly—usually long before startup, and aircraft cabins are typically well ventilated.

The core blendstock and additive packages for 100LL are also different than for automotive gasoline - I'm not 100% solid on the specific chemistry, but I know the hydrocarbon ratios are different, and I believe there's no oxegenating agent (MTBE/ETBE) in avgas, or it's present at a much lower ratio than in conventional automotive gasoline (and obviously ethanol as an oxegenating agent is a no-go as it's incompatible with most aviation fuel systems, and that's a noticeable part of the familiar "(automotive) gasoline" smell most of us know).

Yes, I was using that term in its non-aviation sense for generic motor vehicle fuels (I've modified my comment to be more specific since I wasn't quite at the maximum character limit for a comment :-)

@voretaq7 Roger. Comment deleted as obsolete


text:
Why are some LNAV/VNAV mins lower than the LPV mins for the same approach?
Why are some LNAV/VNAV minimums lower than the LPV minimums for the same approach? See the RNAV (GPS) Rwy 5 approach at Scott Municipal (KSCX).

Because TERPS criteria are weird and don't always seem to make much sense.

What's even more interesting is that the VGSI (PAPI) GP is below the RNAV GP...

From what I could find out, it looks like they're unusual cases produced by the obstacle clearance calculations. There's a lengthy thread on PoA about it and the main points I saw are:

LNAV/VNAV and LPV approaches are designed differently (the specifications are in FAA Order 8260.58)
The Obstacle Clearance Surface (OCS; an imaginary zone that must be free of obstacles) is shaped differently for each approach type
The OCS isn't at a fixed angle: it depends on the designer's choice of glideslope angle (e.g. for terrain clearance) and - in the case of LNAV/VNAV - on the prevailing temperatures at the airport
The two approach types have decision points at different distances from the runway threshold, which also affects the glideslope requirements
The resulting OCS may be at a higher angle for LNAV/VNAV than for LPV

The FAA Order has a lot of formulae to work it all out, but apparently the result is that if the calculations come out in a certain way and there's an obstacle close to the runway, it can penetrate the LPV OCS but not the LNAV/VNAV OCS. That means the LPV DA then has to be made higher.
In the PoA thread, every example of an approach with LPV minimums above LNAV/VNAV has an obstacle close to the runway. But the consensus was that the LPV minimums being higher than LNAV/VNAV is still very unusual overall.
Finally, although this isn't exactly the same scenario, an old FAA article on GPS approaches mentioned that the minimums aren't always what you would expect:

While [varying the obstacle clearance for an LNAV/VNAV approach] occasionally results in minima higher than the LNAV
  minima, the added safety benefit of a stabilized descent outweighs the
  difference in minimums

(That all refers to altitude, of course. The other part of the minimums is the visibility, but that should increase anyway as the DA and/or category increases. A high, fast aircraft needs to be able to see the runway from further away in order to descend safely.)

I saw an excellent answer here: http://www.askacfi.com/3854/lnav-lower-than-lnavvnav.htm
(when you look at the page look for 'LPV')
and as it looks to me it has to do with the width of the area evaluated for obstacles that is taken into consideration.

We try to avoid link-only answers here in case the link breaks, and it's also easier to add comments and explanations. If you can expand a bit on the details of the obstacle considerations, it could be a good answer.

That article addresses why the LPV is generally LOWER than LNAV/VNAV, without discussing a case as asked here where the reverse is true. That atricle is answering the question how an LNAV minimum can be lower than an LNAV/VNAV minimum to the same runway, which it does, although it also brings in LPV as being generally the best solution. Which it generally is, although this doesn't really address the question here.

Good point.  So the question in itself should have been flagged for 'why is something true' when it is really false?  So, if LPV is seen as the best approach method and yet other approaches have lower minimums I suppose I would edit the question to say something like 'do lower minimums imply a more dependable type of approach'.?


text:
Is King Khalid International Airport in Riyadh actually very big?
Apologies in advance if this is in the wrong place, there isn't a geography StackExchange so this was the next best option I could find.
I've read multiple things about the huge size of King Khalid Internaional Airport (IATA: RUH, ICAO: OERK) in Riyadh, one source said it was bigger than Paris and others have said it's larger than the entire country of Bahrain.
Judging from Google Maps, it really isn't particularly big. What's the deal with that?

Not sure if this is on topic, but it certainly is amusing.

By the way, [skeptics.se] exists for testing the validity of claims, regardless of their domain. You just need to have a 'notable' source for the claim. You don't necessarily need to move this question there; I just wanted to let you know about it for the future, since you mentioned looking for the proper stack.

The answer to this question will depend to a significant degree on how the airport boundaries are defined. In the case of King Khalid (OERK), the supposed airport boundaries—encompassing some 230 km²—consists primarily of undeveloped land as well as a University, research centers, and residential developments. To my mind a more accurate aviation-specific definition for the term airport boundary would more along the lines of: airport land surface dedicated to aviation use, support of aviation, or set aside as area protected for aviation purposes.

The King Khalid International Airport (234 km^2) is larger than Paris proper (160.0 km^2).
The King Khalid International Airport is not larger than Bahrain (762.8 km^2).

To arrive at this answer I used some data from various sources.  Mostly non-official but dependable sources as I do not have the language skills to navigate Arabic websites.
I pulled street data from OpenStreetMap and using the very good find by the community wiki response georeferenced the future land use map with points using the polyline data.  Georeferencing is used to correctly orientate and scale raster images to geographical locations.  I then created a new feature using the rubbersheeted/georeferenced land use map to draw the rough outline of the land that could be used for airport activities; this is the land dedicated to airport use not necessarily the actual size of the facilities.  This should give us a rough idea of the size and shape of the airport.  234 square kilometres.
Using data of the administrative districts for Paris, I summed the area of the 80 districts for Paris proper.  160.0 square kilometres.
Using ESRI's shapefile for world nations, I found the area of Bahrain.  762.8 square kilometres.
If you enjoy maps, come on over to the https://gis.stackexchange.com/.  It is probably the closest to pure geography on SE yet.

So basically the consensus is the size is based on the airport's land area?

Truthfully not sure what the exact definition of an airport facility would be and if it wouldn't change country to country.  I am not associated with the air travel industry in any form, but love this SE and first question my skills (GIS/Urban Planning) could help with.  Without an official definition or map boundaries, land use is probably the safest bet as usually air use zones forbid most construction and use owned by the  facility.

It depends how you define the airport. I don't think your Google Maps method is sound, however; it depicts built-up areas, not the airport boundary. You couldn't draw the same map around LAX, say.
The standard for measuring the area of an airport appears to be the total land owned by the airport. And jet age airports, with their expansive noise buffers and office park reservations, tend to take as much as they can get. DEN is reckoned the largest airport in the U.S., at 33,531 acres (~136 km²), though only a fraction of this is developed.
The numbers for total land are easy to find, the numbers for improved land less so, but I found an informative Globe and Mail article about Montreal-Mirabel. When originally created, the land seized for the airport was larger than the city of Montreal itself— around 97,000 acres (~392.5 km²). The article notes that the airport perimeter itself was only about 5,200 acres (~21 km²). Still, it's the former number that is commonly bandied about, and the measure by which Mirabel was considered the largest airport in the world.
According to Kable, a London-based business information firm, King Khaled International Airport covered an area of 225 km² when it opened in 1983.
In 1999 it was surpassed by King Fahd International Airport, which occupies 776 km². This is roughly the figure given by the 2013 Guinness Book of World Records.

It might help to have citations for the claims you mention - perhaps there's missing context.
That said, you're right. The comparisons sound utterly false, based on Google Maps' measurement tool:

Click to embiggen the images, but they're not remotely close: Bahrain's total area is around 700km²; OERK airport according to Google measures closer to 37km². It's not even necessary to closely follow the Bahrain coastline to get a precise figure, the numbers are so far off.
That said, Wikipedia has an uncited claim that:

The airport occupies an area of 375 square kilometres (93,000 acres).

It seems likely but not guaranteed that this could be due an omitted decimal (37.5km², not 375km²) or to unscrupulous edits. Even so: if it were 375km², it would only be larger than the administrative center of Paris (105km²); it would remain smaller than Bahrain.

EDIT: that seems likely. Back in 2013 an anonymous user added that its area was 300km² and the airport's size has, at least in print, steadily increased since then. I imagine if you did some more forensics you'd find that this is all random IPs.

Or it could be something meaningless like the "amount of land owned by the airport holding company".

I originally read it (the "larger than Paris" claim) in a book published by DK (Dorling Kindersley) called "Amazing Facts" and decided to Google for more information, which I couldn't find much of to be honest.

@GregHewgill it could, but the lack of citation for such a bizarre (and vague) claim, and the various changes over time (300, then 310, then 375) make me think it's just internet weirdoes screwing around.

May be like the Chinese claim that he Great Wall is visible from space... nonsense, but sounds good for national pride.

@RalphJ Lots of things are visible from space, especially roads, but even runways, bridges, etc. in some cases. The Great Wall is indeed more questionable, though. There are some photos where it's a bit visible, but most astronauts seem to say it's hard to see with the naked eye from LEO. Of course, the original claim about it being visible from the moon is utter nonsense.

Yeah, with the right satellite, all sorts of small things are visible from space.  But the Great Wall is thin & narrow, and claims of seeing it with the naked eye are bunk -- which was essentially what the PRC was claiming.

Not a complete answer, but possible airports limits, based on zoning data, may be these one:

Source
Other clues may be discovered in the same page. The cadastral information is handled by MOMRA. The company that surveyed this area may be Twozan.
This is a "community answer", so feel free to improve it.

It really depends on how you define 'big.'
In terms of size of the terminal and movement areas, it's not very big at all for an international airport. Even medium-sized passenger airports in the U.S. are commonly larger than Riyadh's airport. It has only 2 parallel runways and 24 boarding bridges. By comparison, the medium-sized airport I usually fly out of in the U.S. has 36 boarding bridges, 3 parallel runways, and an additional crosswind runway. The busiest airport - Atlanta International - has over 200 boarding bridges and 5 parallel runways in simultaneous use.
In terms of land area, especially land area owned by the airport rather than just what it actually uses, it is indeed quite a bit of land, though that's not necessarily unusual, especially for newer airports built in places with a significant amount of available land. Airports generally like to buy up as much land as feasible in order to have room for future expansion. Many of today's large airports are now space-constrained as the cities they serve have built up around them since the airport was originally built. Airports that can try to buy up land that they might possibly need in the future in order to prevent running out of space to expand.
In terms of passengers per year, Riyadh's airport is relatively large, but nowhere close to the world's largest hub airports. In 2015, Riyadh served 22.5 million passengers. By comparison, Atlanta had 101.5 million. The 50th-ranked airport was Minneapolis/St. Paul International at 36.6 million. So, by passenger traffic, Riyadh is probably somewhere around 100th worldwide, though exact rankings below 50th aren't made public by ACI.


text:
What is the glide ratio of a DA42?
I was looking for the best glide speed of a DA42 with both engines out, but it seems it's not in the POH. In the emergency checklist, it only mentions a speed of 85 knots to maintain on final approach with landing flaps.

In case no information can be derived from the usual sources, (as the POH) the best glide speed can be obtained by finding the maximum endurance speed (the speed that gives the minimum variometer reading when gliding with the engines at idle) and multiplying it by 1,32

@xxavier, where did you get the number 1.32? The ratio between best gliding range and best gliding time speeds depends on the lift/drag ratio.

@Jan Hudec  The ratio of 1,32 (more precisely, the fourth root of 3) is the quotient maximum range speed/maximum endurance speed. Hence, if you determine experimentally the maximum endurance speed by watching the variometer while gliding with the engines idling, you can derive the maximum glide speed just by multiplying the maximum endurance speed by 1,32...

@Jan Hudec  I forgot giving the references. A derivation can be found here http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node99.html   And another one here  https://cafe.foundation/v2/pdf_tech/MPG.engines/AIAA.1980.1847.B.H.Carson.pdf

@xxavier, that only applies to powered best range and endurance speed and only valid for piston-powered propeller aircraft. Best gliding time speed is the same as best endurance, but best gliding range speed is different from best powered range speed.

@ The ratio is valid for any airplane. Read the references, and you'll see that the power used may be of any type, piston-powered, jet-powered, or 'gravitationally powered', as in a glider. For any type or size of airplane, the ratio [speed for max. range] / [speed for max. endurance] is 1,32...  Thus, a pilot may determine the speed for max. range by gliding and observing at what speed the variometer gives a minimum value, and multiplying that speed by 1,32     The min. variometer corresponds, in a glide to the least 'rate of consumption' of pot. grav. energy, i.e. the least power required...

@Jan Hudec  Besides, please note that the OP asks about the 'best glide speed with both engines out'. Obviously, in that condition the plane is gliding, and when gliding the only power available is that derived from 'potential energy consumption', i.e. loss of altitude. And the rate of loss of altitude is measured with the variometer, so the minimum reading of the variometer corresponds to the speed for minimum power, i.e. the speed for maximum endurance... You take that speed, multiply it by 1,316... and presto! you get the speed for maximum range...

@xxavier, You take that speed, multiply it by 1,316 and you get the speed for maximum range powered. Maximum range gliding is different.

@Jan Hudec Different...? Explain why...


text:
What would be the advantage of a Puller vs. Pusher configuration on Embraer's new Turboprop?
Embraer recently teased a turboprop aircraft with aft-mounted, open rotor engines. Why would this aircraft not use a pusher configuration?
The reasons that are frequently stated as a benefit for a wing-mounted, pull configuration (e.g. avoidance of disturbed flow from the wings, blown lift over the wings, control surface effectiveness, etc.) would not apply here. To the contrary, it seems to me that re-energizing the exhaust/wake of the engine and maybe to some extent the fuselage would have a beneficial effect.
One possible reason could be that Embraer would like to use an existing engine. In that case turning it around would point the exhaust forward and the intake backwards. That, however, also seems to be a solved problem: the MQ-9 uses the Honeywell TPE331-10GD turboprop engine, which is designed for a pull configuration. Another might be ground clearance during rotation.

Maybe reword the title question to ask about advantages or disadvantages of each design?  Just a suggestion...  Because I don't think there is a verifiably "correct" answer that won't be opinion based.  Unless someone here is an inside part of the Embraer team, and is willing to publicly share the company's rationale for making the decision.

@ymb1 & Michael Hall: Thanks - edits made.

You will almost certainly get a buzz noise from the  wake of the nacelle's pylon.  The puller layout will be definitely quieter and it also moves the CG forward a bit compared to prop at the back.

@MichaelHall A design process leading to a configuration should not be defined as being opinionated.

@Koyovis, I agree, but the original question wasn't about a design process, it was about their business decision, i.e. "why did Embraer decide...?"  Hence my comment, which is N/A since the edit.

No need to turn the engine around for a pusher config.

Pusher configurations often run into clearance issues. The landing gear is usually further forward of the prop, and while taking off, or flaring to land, the prop has to have enough clearance to avoid prop strike. Usually this is solved by bigger landing gear (more mass) or placing the engine higher (thrust misalignment + usually more mass) but ultimately both solutions lead to the ability to use a larger radius propeller in puller configuration, and the bigger your prop, the better efficiency, so why not use the pusher configuration?

You mentioned an engine that can be used for pusher prop configuration, but, when it comes to mass production and corporate supplier relations - that engine might not be available to Embraer. For instance - Honeywell has an exclusive contract with, say, Boeing or Airbus for that engine. Or - Honeywell cannot produce enough of those engines to fulfill a contract with Embraer, and they are perhaps phasing the engine out for a variety of reasons, so they have no wish to increase production.

Engine cost. Continuation of pt.2 - most turboprop engines are designed to be pullers. This means that they will have a decent amount of common components. Turboprops for pushers are not as common, so there would be a larger amount of unique components, which would drive up design and production costs, as well as maintenance and sales costs.

"and they are perhaps phasing the engine out for a variety of reasons, so they have no wish to increase production" - in that case, no reason they couldn't sell the design to Embraer to produce in-house.


text:
Are there examples of taildragger autoland systems?
I have only been able to find examples of auto-land systems for tricycle gear. Is there an equivalent for taildraggers?
I realize taildraggers are more commonly used in VFR conditions, so there may not be a sufficient market draw solely based on the weather argument (as would be the case for e.g. commercial air transport). I also realize that taildragger aircraft tend to cost less, thus making it harder to justify investment in an avionics capability that would likely be expensive. But are there any other reasons why they are so much less common (if they exist at all)? The physics would be different, but modern control systems are capable of handling those...
Follow-Up Feb 23: Since there seem to be no obvious examples - and in light of the constraints identified above and in John K's answer - what would be the simplest (read: cheapest) taildragger auto-land system that would provide meaningful benefit (e.g. prevent ground loops)? For example, would a simple "Heading Hold Mode" augmentation system be helpful? If not, why not?
Fun Fact: The closest to a "landing system" that I could find is Brodie Landing System for the L-4, discussed here.

There aren't any tailwheel airplanes with the level of sophistication that would make it even worthwhile doing.
It could be done in theory but would require a much more sophisticated system because taildraggers are considerably more demanding to land and to control on the ground (they are dynamically unstable while rolling on the ground and want to switch ends - try pushing a shopping cart backwards really fast).  There just isn't a market that would even take an interest in developing it.

It seems to me that being dynamically unstable would make it even more attractive for a control system? The X-29 comes mind...

Point is I'm not aware of any taildragger airplanes where one would even think of certifying Autoland.  There are very few that fly IFR at all... Beech 18s, DC-3s, from time to time.  Think anybody's gonna develop an autoland for the DC-3?  Might as well include a booster rocket for low orbit as well.

The important point is that autoland currently means ILS and when that is constructed, the runway can also be paved, but the only practical advantage of tail-draggers I can think of is for rough fields.


text:
Can multiple airfields be in the same airspace?
After reading this answer that a restricted airport caused a strange cutout in Class B, I am wondering if it possible that there are multiple airfields in the same airspace?
If yes, then:

Which ATC has most authority
How congestion is handled?

Please note that I am not talking about an airport which is under an outer circular shelf of a Class B or C airport.

When there are several airports close to each other, a single ATC, formally known as Terminal Control Center may service all airports. The airspace boundaries and altitudes assigned to a Terminal Control Center, which vary widely from airport to airport, are based on factors such as traffic flows, neighboring airports and terrain.
London Terminal Control Centre is an example of a large and complex Terminal Control Center. Its service area is up to 20,000 feet and out to 100 nautical miles. It controls:

six London airports
one Royal Air Force station
provides en-route services to other aircraft that entered its airspace

Another example can be found with Berlin-Tegel and Berlin-Schönefeld, which have adjacent control zones that share a common boundary west to east and have an overlaying class C TMA airspace up to FL100. Both airports share the same TMA controller/approach sector:BREMEN RADAR Approach:    119.62
Image Source: www.skyvector.com

FAA is implementing a new airspace system which will increase efficiencies at metropolitan areas with complex air traffic flows. This system, known as Next Generation Air Transportation System is introducing the concept of a metroplex:

In FAA parlance, metroplex refers to a system of airports in close
  proximity and their shared airspace that serve one or more major
  cities. A metroplex has at least one, but often two or more major
  commercial airports.

this is already done in Norcal: https://www.faa.gov/nextgen/snapshots/metroplexes/?locationId=14


text:
What happens if a passenger dies mid-flight?
Last month (December 2014), there were news that a passenger passed away during a flight. As mentioned in this answer, it appears that it is not a very uncommon scenario.
In an unfortunate incident like this, how is this matter handled?

This is dated info, applicable in the 1990s to Hadj charters in 747s, so I'm putting it as a comment. On these flights, deaths were not uncommon. Most of my Hadj flights were Jakarta to Mecca and return, with a few from Indian airports to Mecca and return. We carried body bags, and the body would be bagged and laid out in the rear of the cabin. The flight would continue to the destination. There was a doctor on each flight who could, in theory, ask for a diversion, but they never did. As I understand it, to die while performing the Hadj was believed to be a blessing.

In the event of a passenger dying on an airplane during flight, each case is different depending on the location of the airplane, the duration of that flight and the wishes of family or friends traveling with the deceased passenger.

What happens to the flight?
If the death occurs before takeoff or shortly after takeoff, the airplane is landed back to that airport or the nearest airport. If it happens mid-flight, normally the flight is continued to its destination.
Where is the deceased passenger placed?
If there is a seat available in first or business classes, the deceased person is moved there and covered with a blanket. If it is a full flight, that person may simply be strapped in more tightly and covered. This is done to ensure that the body is out of view of other passengers. A deceased person is never placed in the lavatory. It is not respectful and a major security concern.
What happens at arrival airport?
The arrival airport is informed in advance about the situation. Hence police, ambulance and coroner are available. Some airlines keep body bags on board. Normally the deceased person is placed on a stretcher and is carried from the rear exit of the airplane using a lift truck and then placed in an ambulance. This might be done after other passengers have exited the airplane.
What are the regulations?
FAA have regulations addressing several emergencies, but not specifically this one. An FAA spokesperson mentioned:

FAA spokesman Les Dorr said he was unaware of any policies that
  specifically address what should be done if someone dies in flight.
  The airlines make those decisions on their own.

This article mentions some incidents of this situation happening.
MedAir is a company which provides airlines with medical help from emergency care doctors on the ground. They estimate that:

... there is one death for every 8 million passengers from the airlines [they] serve ...

"One death from every 8 million passengers" - an interesting stat, as (taking statistics alone) it means you're roughly 2-5x more likely to "just die" on a flight than to die in an airplane accident.

@Jon I wonder how likely they would be to "just die" if they weren't on a flight ...

Think about all the person-hours collectively spent on flights every day...that far exceeds the typical human lifespan, even though getting on an airplane requires a certain degree of health and removes several hazards that kill people elsewhere.

Twenty years ago Singapore Airlines installed a special locker in their A340-500's which could be used if a passenger died on their ultra-long Singapore to Newark and Singapore to Los Angeles routes. According to a U.K. Guardian article from 2004:

The airline's new fleet of Airbus A340-500 aircraft boasts a discreet locker next to one of the plane's exit doors which is long enough to store an average-sized body, with special straps to prevent any movement during a bumpy landing.

Cabin crew have been instructed to use the locker in the event of a death on a long-haul flight - particularly if the aircraft is busy, with no free seats on which to lay out the deceased.

The aircraft came into use in February, operating the longest non-stop route in the world: a 17-hour, 7,900-mile journey between Singapore and Los Angeles.

Singapore Airlines operated their fleet of five A340-500's for ten years, and some reports say that the lockers were never used, however I'm not sure if it's possible to know that for certain. A Simple Flying article says that an airline spokesman told them that it "was likely never used", however that is far from being definitive.

Flight attendants are not allowed to declare someone dead so they would continue giving care until either (STAT-MD or A medical professional) declares them dead they would be put in a empty row or in first class (if flight is full they would be put back in their seat with blanket over them.

Wait a minute, you are saying that if someone dies mid-flight and there is no doctor on board the flight attendents have to do CPR until physically exhausted?

There's another 100 or so pax on board, @quietflyer, they can take turns...

@quietflyer yes, but (STAT-MD) can also do that they are a medical center 24/7 and can connect through the cabin medical headset and give instructions and declare death

Oh, ok, guess I had no idea what that was--


text:
Are there any safety features to prevent reversible-pitch props from reversing in flight?
Some aircraft have propellers capable of reversing pitch, which is also known as beta angle. The example I saw was an Aviat Husky.
(Youtube demonstration)
I want to know if there are any safety features that prevent this from activating while airborne. For example, what kind of controls activate it? How long does it take to actually reverse the blades, and how much physical effort does the pilot have to exert? Would it be impossible to force the reverse when at high cruising speed?
If it is a mechanically powered reverser, then is it possible for it to be inadvertently triggered?
And if it is activated, can it quickly be set back to original blade angle?
Note, I am interested in any propeller-driven aircraft, not just commercial ones, but smaller ones as well. Piston prop, turboprop, GA, anything.

Beta props are pretty rare on anything smaller than Twin Otter or King Air or Porter or Turbo Beaver.  Can't speak for MT's system, but most beta mode systems use mechanisms to switch control of propeller blade angle from the propeller rpm governor to the throttle.  Beta mode is the mode of throttle or power lever control of blade angle, with engine torque controlled by a governor system of some kind to regulate rpm.
Beta mode is very similar to turbine helicopter collective control, where a lever, the collective, directly changes rotor pitch and a governor system regulates rotor rpm by adjusting engine torque.
Beta mode is normally entered just above flight idle (flight beta) once the propeller speed governor is no longer regulating blade angle (blades at fine pitch stops).
There is normally some kind of detent or gate that requires a deliberate movement or unlatching to move below flight idle (the Twin Otter requires you to twist the throttle grips - on others there are finger triggers).
Also, some turboprops have beta lockout systems that prevent power lever movement below flight idle until you're on the ground.  But a lot of airplanes don't and can be put into ground beta in flight if the flight idle gate or latch is deliberately operated by the pilot.
During the Twin Otter program there was some controversy at DeHavilland Canada because demo pilots were using ground beta (coming into DISC - blades flat, like a disc) to make crazy steep descents (I've also heard of Porter pilots doing it).  A very dangerous thing to do, because if the prop doesn't want to come out of beta mode when you move the lever(s) back up, you are dead meat.

I have heard of C130 pilots (the ones who were flying the landings onto the Forrestal in particular, but perhaps this is more general) using beta/reverse basically in the flare to achieve very short landing distances, which makes me wonder how the Herc handles all this...

So once it's engaged, then at full throttle you're at full reverse pitch, and at half throttle you're at half reverse pitch?

More recently, the Let L410 has been having issues with beta mode engaging uncommanded, like in this accident: http://avherald.com/h?article=4b111511&opt=0

@DrZ214 yes but the range is in the other direction from normal.  At flight idle, the blades will be a the now pitch limit for constant speed operation.  As you move the power lever AFT from flight idle, the blades get finer and finer in direct relation to the power lever movement.  At DISC, the blades are flat.  Farther back moves them into reverse pitch.  You move the power lever/throttle and the blades move.  Meanwhile, rpm is now controlled by a speed governor that regulates engine power to the propeller  to keep a predetermined rpm schedule as the blades move into reverse.

The aircraft I fly has a constant speed, reversible prop with beta.  It has several protective devices to prevent the blade angle from decreasing.  The main ones that you're interested in are the low pitch stops and the flight idle stop.
The low pitch stop is essentially a latch inside the prop dome that prevents the blades from going into the beta range by blocking the pitch change piston.  It can be overcome by an increase in oil pressure (260-310 psi on ours).  Normal operating pressure is between 150-250 psi, but we don't have a gauge to verify that.  The additional hydraulic pressure is not available unless a valve inside the prop control mechanism is opened, which happens when the pilot pulls the power levers into the ground range.  The power levers do many other things, and one of the nice things about the P-3 is that you don't have to deal with prop levers or condition levers.  But I digress.  Low pitch stops are more likely to fail in the engaged position, which would prevent reversing the prop altogether.  In flight, it would take a failure of several other prop protective devices to even get to the point where they are needed.
The flight idle stop is a solenoid-activated stop that makes it more difficult (though not impossible) to pull the power levers into the ground range and reverse the blade angle.  It is energized and pulled out of the way when the plane touches down and when the power levers have been pulled "over the ramp".  If the solenoid fails it takes an addition 12 lbs of force to overcome it.  The flight idle stop additionally prevents the prop control from going into revers should the power lever linkages break.  Occasionally the solenoids come apart entirely, which prevents you from going into reverse.  At that point, you feather the engine to prevent forward thrust while you're trying to stop, or else you're going off the end (or the side) of the runway.
"Over the ramp" refers to the fact that the power levers need to be lifted up when they are at flight idle to get into the ground range.  If you really wanted to, you could overcome everything and put the prop in reverse inflight.  At that point, the negative torque (-500 to -1700 shaft horsepower) should activate the safety coupling, disconnecting it from the engine.  The prop would overspeed severely, and could conceivably throw the blades right out of the hub if the RPM got high enough.  You have to be going pretty fast for it to get that bad though.


text:
Can VOR indication be reliable if one of its antennas breaks?
What will be the reliability of the VOR indication inside the cockpit if one of the two outside antenna is broken ?
Can we trust it to make a VOR approach?
What will be the consequences assuming that we are in a general aviation aircraft like cessna 150 / 172 / 182 .
Picture of antenna:

(Image Source: http://www.simmer.fr/)

No, it should not be used.
Twin antennae, as you have shown, are balanced and fed into a balun (BALanced to UNbalanced) to feed the single transmission line to the receiver.   Together, they provide the correct impedance for the aerial system.  With an antenna broken, it is likely that the impedance of the circuit is wrong and therefore, the input to the receiver is, at best, suspect.
[GUESSWORK]
It's impossible to predict the indicated behaviour without knowing precise details of the aerial fit but a reasonable guess would be that the standing wave ratio in the feed will be altered and therefore, a phase error will be introduced.  The magnitude of the error will vary in proportion to the sine of the actual phase angle so my guess would be that the bearing will be accurate when due South or North of the VOR then increasingly inaccurate as you move round with an maximum error at 90 or 270.
[EDIT]
Early in the morning when I first wrote this but I think I am wrong about being accurate due North or due South.  It will be accurate somewhere on the compass and at 180 degrees opposite to that, with increasing inaccuracy as you move towards 90 degrees away from that somewhere.  Only calibration would tell you where the somewhere is.

Losing one pole of the VOR antenna can indeed cause a phase offset in the signal - at the very least it mucks with the dipole pattern of the antenna. You'd be amazed how well a VOR receiver can work when both of the cats-whisker antennas are snapped off though (this happened to the plane I did my training in as a result of "a freak plane-washing accident" -- the receiver actually worked BETTER that way). Of course being that the antenna is damaged that still leaves you in a situation where you shouldn't use it.

The literal answer is, who knows? The only way to find out for sure would be to calibrate the VOR and observe the deviation - if any - from the expected readings. The instrument manufacturer might have some general guidance, but no one can predict the results of physical damage accurately.
But having said that, it doesn't really matter anyway: you shouldn't be doing anything that requires a VOR if you know that the equipment is broken. Even if it still seems to be accurate despite the missing antenna, what happens if you lose the other antenna? Or some broken wiring starts causing intermittent false readings?
And although this is getting away from the exact question that you asked, there are regulations to consider. You didn't mention a specific jurisdiction, but let's assume US/FAA for now, I'm guessing the general rules are very similar in most places. If you're VFR then you don't need a functioning VOR anyway: by definition, you will never be relying on it for anything because you're navigating visually. It might be helpful to have a VOR in VFR, but it isn't required. (14 CFR 121.349 does allow for VFR flights on routes where you can't use pilotage, but it also requires two independent navigation instruments.)
On the other hand, if you're IFR then it would probably be illegal for you to rely on a VOR that you know is damaged. 14 CFR 91.205 requires "navigation equipment suitable for the route to be flown", and I think it would be difficult to convince the FAA that a VOR with a broken antenna is suitable for navigation.
But the most basic point of all is that relying on broken equipment is just dangerous, especially for an instrument approach where you're relying on the accuracy of the instruments to prevent you from colliding with the ground or an obstacle. In my opinion, taking that chance would show very poor decision-making and general airmanship.

The only effect of a broken VOR antenna is that the polar pattern of the antenna will be altered, and its efficiency as an antenna decreased because it will be mismatched to the feed line. This means that you may only pick up the VOR when the "good" antenna element is closest to the beacon, and its lower efficiency will mean that the range from the beacon you get a signal will be decreased.
The navigation information is all carried in the 30 Herz modulation on the main carrier and the FM subcarrier: nothing in the VOR receiver ANTENNA can affect the phase relationships of the 30 Herz.
If the warning flag is not showing, there is adequate signal and the VOR bearing will be accurate.
Not good practice to leave an antenna broken in this way, but it is not an issue regarding safety as long as you've got enough signal (i.e. no warning flag).
Exactly the same applies if you're receiving an ILS localizer - the information is in the 90 and 150 Herz modulation in this case.  As long as the warning flag isn't showing the information WILL BE ACCURATE.

+1 on the relevant thing. The antenna damage only affects useful range. As long as the warning flag is not showing, the instrument will be accurate.

"The antenna damage only affects useful range", yes that seems correct to me too.

VOR's direction doesn't come from the aircraft seeing where it comes from.
VOR works by a pulsing omni-directional beacon and a sweeping narrow beacon. The pulse happens each time the sweep is north. Then the heading from the compass is used to see where the beacon is relative to the airplane.

(Image Source: Wikipedia - Author: Orion 8)
Does this mean that you can use it for navigation with a missing antenna?
Not unless the system was designed to compensate for a missing antenna.

This doesn't seem like a complete answer to the question. You show that a single antenna is able to receive a VOR signal, but is it safe to use? Will it be accurate enough?

-1 I agree with raptortech97, you can't screw with the engineering, don't allow a little knowledge about how something works to temp you into thinking you know better. I can't count the number of Flight Safety courses I've attended where student try to out-smart the design of the aircraft. Go by the book; if something is broke, fix it!

@raptortech97 I amended the answer to add that.

I don't think this answers the question, but it is the best description I've seen on how the VOR system allows a plane to figure out where it the world it is. If I were to post a "How does VOR work?" question, this would likely be my accepted answer!

That's not a very accurate description of how a VOR works.  This has a better descriptionHow does TACAN Work?

Short answer: no.
In general, if a piece of equipment has an operability issue, it should not be used for navigation.
That said, if you test it and the test indicates it is functioning reasonably, it may be ok to use it on SHORT TERM BASIS. So, for example, if I were taking off from Manchester I would fly up to the Cordcord VORTAC and see if I were getting reliable readings. If so, I would probably feel ok using it on a VFR approach.
In any case, the antenna should be fixed before using the instrument long term. To use the receiver with a damaged antenna once or twice is excusable, but not for an extended time.
Note: By "reliable" readings I mean you are receiving a signal at different attitudes, or at least in the attitude you need for navigational purposes. The effect of a broken antenna will be to reduce your gain or possibly introduce a blind spot into your reception area. Note that these effects are ALWAYS present anyway. For example, in mountainous terrrain or if the VOR is straight ahead you could have blind spots in the VOR even with a perfect antenna. So, a broken antenna basically just makes standard reception problems you already have, worse.

Using it as a source of navigation at all would be irresponsible period.  There are two antenna for a reason, otherwise the manufacturer wouldn't have them both there.

@Lnafziger Its easy to sit back in your chair and lecture somebody about how their aircraft should be perfect and you should never use so much as a cracked anything, but in the real world sometimes you need to use an imperfect piece of equipment. What if the guy is at a remote airfield? Tell him to use dead reckoning? Is that your plan? A VOR with one antenna is a lot better than dead reckoning I can tell you that. Sometimes you have to fly with a lot more busted than one antenna.

@TylerDurden The consequences of using a malfunctioning VOR can be pretty severe (like "Wandering into restricted airspace because your bearing was wrong" severe) if you're using it for primary navigation, and as Simon noted it may work fine on one bearing but be off on others. In your hypothetical situation I would tell the stranded pilot to wait for a good VFR day, pull out their chart, and rely on good old-fashioned pilotage to get them home (or more likely in this 21st century of ours point at their smartphone and remind them they have a GPS in their pocket they can use to help them out).

@voretaq7 A damaged antenna is not the same thing as a "malfunctioning" VOR. The effect of a  damaged antenna would be to reduce its gain. The typical bad outcome would be that you might get no signal. Simon's idea that it would somehow affect the accuracy of the signal is completely wrong. The phase shift on VOR is to the modulation frequency, not the carrier frequency. Basically he has no idea what he is talking about.

@TylerDurden I think 10 years as an avionics engineer gives me a reasonable background to comment, it addition to having done troubleshooting on such problems using some quite advanced signal analysis tools.  But since my professional knowledge is incorrect, I would welcome knowing what your credentials are and exactly why the problem of the standing wave ratio being altered is incorrect.  Were there one antenna, I might agree but given that one of the two in a balanced system is damaged, the change in gain is a secondary concern.

@TylerDurden By the way, if a VOR signal were amplitude modulated, I would again agree with you, but since it is frequency modulated, and the direction is determined by the phase angle between the fixed reference signal and the modulated signal, then any change in the SWR must introduce a phase error.  I guessed, hence the tag in the answer to alert readers, that for any given error, there must be two points on the sine wave where the error is 0 and 2 points where it must be greatest. However, I could be wrong, but without knowing the exact fit, and exact physical problem, impossible to say.

@TylerDurden  I have a typo in my first comment to you.  In fact, I spent 20 years as an avionics engineer.  I have also just checked my log book.  I found a problem on a Vulcan in 1981 with different symptoms and a different cause, but easily extrapolated to the OPs question.  The symptom has that the VOR would track well, but would then swing to about a 30 degree error for a while, then swing back.  We could not reproduce the fault but changed the receiver to no effect.  Using a TDR, we found a bad connection in a bulkhead.  Remade the connection and the fault did not reoccur.

And also, the question says a BROKEN antenna, not a damaged one.

authors: عمران الشلبي


text:
Did the Stuka Ju-87 really have a radio altimeter? If so, when?
This is what Wikipedia says near the end of its radio altimeter article:

The radio altimeter first showed up in the German Junkers Ju-87 "Stuka" dive bomber which was equipped with one for automatic pullouts in the dive bomb run which usually consisted of an 80-90 degree dive. The Stuka pilot would set the radio altimeter to 750m which was connected to the bomb release and automatic pull out. The radio altimeter would drop the bombs and pull the Stuka out of the dive at the set altitude to a level flight. This was invented because the pilots would black out on the pull out, usually for 2 to 5 seconds.

No citation, and I would be skeptical anyway. I know the Stuka had an autopilot that pulled out of a dive, but I thought it was activated manually by the pilot dropping his bomb. I figured he would just drop his bomb at whatever altitude he judged by his own eyes, rather than watching some altimeter instead of the target.
I'll also note that Wikipedia is not self-consistent here. If you scroll up just a few paragraphs, it says:

In 1924, American engineer Lloyd Espenschied invented the radio altimeter. In 1938, Bell Labs put Espenschied's device in a form that was adaptable for aircraft use.[13] In 1938 in co-operation with Bell Labs, United Air Lines fitted a radar type device to some of its airliners as a terrain avoidance device.[14]

Two citations there. So I don't know what the author means exactly when saying it "first showed up" in the Stuka.
I would have thought such a radio altimeter would have been very difficult without the cavity magnetron, invented in Britain and sent to America in the Tizzard Mission of 1940 September.
On the other hand, I have come across some night fighter radars that Germany had, such as the Lichtenstein Radar that did not need cavity magnetrons. That was not used until 1942, though.
So did the Stuka really have some radio altimeter? If so, when? Was it really the B version that saw action in 1939? What frequency and power did it use? How big was it?

A radar altimeter doesn't require nearly as powerful a transmitter as an air defense radar. The ground is a much larger target than an aircraft, and it's much closer. So you don't need a cavity magnetron.

WW2 also had radar-fused anti-aircraft shells, to further blow your mind https://en.wikipedia.org/wiki/Proximity_fuze#World_War_II

It looks like the actual date is 1942. The 'Nachtschlachtgruppen' aircraft were given Ju 87 D aircraft with numerous upgrades including the FuG 101 radio altimeter.
This would make sense because to use the regular contact altimeter the pilot must have knowledge of the height of terrain above sea level and then add to that when preparing his aircraft for dive bombing. A radio altimeter should always give absolute altitude above the terrain. At night trying to estimate your height above terrain is basically impossible. It's either completely black or a sea of lights beneath you.
I found this information on page 58 of "Junkers Ju-87 Stuka", ISBN 978-83-89450-49-4. More information this book and excerpt is found here: http://mmpbooks.biz/ksiazki/46
Some brief information about the Fug 101: https://airandspace.si.edu/collection-objects/radio-altimeter-german-fug-101-1500-meter-type
https://forum.keypublishing.com/showthread.php?132745-FuG-101-Radio-Altimeter-S-101-Transmitter-Unit

In places where Stukas were doing their thing there was no ATIS to give you field elevation etc (QFE/QNH) to enable accurate determination of altitude.

but there were maps, and determining elevation of the target was one part of flight planning. You know what maps are? No need to charge batteries, no boot time, just a big piece of paper with lots of information on it.